This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Bacteria growing as biofilms, where cells aggregate into a film formed from various excreted substances, grow on surfaces throughout the human body. Biofilm infections are common, and represent a broad range of ailments from infections associated with cyctic fibrosis to tooth decay. These infections represent a particular challenge for medicine because they are notoriously resistant to both immune response and antibiotic treatment. Traditionally, doctors supposed that biofilms'physical structure prevented antibiotics from penetrating to cells in their interior. However, recent research has revealed that biofilms have a complex spatial structure and can harbor a diversity of genetic strains of bacteria, including strains that are resistance to various antibiotics. This evolutionary diversification provides a complementary explanation for the capacity of biofilm infections to resist antibiotic treatments. We propose to study the evolution of antibiotic resistance in biofilms. We will test three hypotheses: H1: Biofilms are resistant to antibiotics because of their physical structure;H2: Biofilms are resistant to antibiotics because of their genetic heterogeneity;H3: Biofilms have evolved resistance to biofilms because of the action of natural selection. H1 will be tested by comparing the levels of antibiotic resistance of intact and homogenized biofilms. To evaluate H2 versus H3, we will develop a simple neutral model for biofilm growth and compare this model's predictions to empirical data. Any deviations from the predictions will represent non-neutral processes occurring during biofilm growth, such as selection for certain bacterial phenotypes.